Field of the Invention
The invention relates to liquid solutions of dicarboxylic acids having 6 to 44 carbon atoms.
Discussion of the Background
A wide area of application for dicarboxylic acids is their use, for example, as a raw material in the preparation of polyamides. An inexpensive preparation process, which eliminates the quantities of water required in the conventional procedure via nylon salt solutions, is to start from melted diamines and dicarboxylic acids. In this case the components are melted, mixed and subjected in the melt to polycondensation. In practice, an important disadvantage of the process is that the dicarboxylic acid cannot be melted without discoloration, and becomes severely discolored on prolonged storage in the melted state. This discoloration is then passed onto the polyamide produced by polycondensation. A product of this kind is not accepted in the market. Aromatic dicarboxylic acids, for example terephthalic acid, cannot be melted at all without undergoing decomposition.
In practice, therefore, polycondensation in the aqueous phase is chosen instead. On the industrial scale, this process requires the heating and evaporation of large quantities of water (EP-A-0 122 005).
For these reasons it is desirable to find practicable ways of carrying out the polycondensation in the melt. The object of the invention was to provide an aliphatic dicarboxylic acid, in the form of a liquid melt, which shows no discoloration even on prolonged storage.